Ishigadine A,a new canthin-6-one alkaloid from an Okinawan marine sponge Hyrtios sp.

A new indole alkaloid with the canthin-6-one skeleton, ishigadine A, has been isolated from an Okinawan marine sponge Hyrtios sp. The structure of ishigadine A was elucidated on the basis of spectroscopic analyses. Ishigadine A is a new canthin-6-one alkaloid possessing a hydroxy group, a 1,3-dimethyl-4-methylthioimidazolium, and a 1-propylguanidine. Ishigadine A is the third canthin-6-one alkaloid from sponges. Ishigadine A might be generated from l-arginine, l-histidine, and l-tryptophan. Ishigadine A exhibited moderate cytotoxicity against L1210 murine leukemia cells.     

Alternating Copolymerization of Ethylene and 5‐Hexen‐1‐ol with [Ethylene(1‐indenyl)(9‐fluorenyl)]‐zirconium Dichloride/Methylaluminoxane as the Catalyst

The copolymerization of ethylene and 5‐hexen‐1‐ol pretreated with trimethylaluminium was performed using [ethylene(1‐indenyl)(9‐fluorenyl)]zirconium dichloride/methylaluminoxane as the catalyst. The 5‐hexen‐1‐ol unit in the copolymer could be increased to about 50 mol‐% with increasing [5‐hexen‐1‐ol/ethylene[ ratio. ¹³C NMR analysis proved that the poly(ethylene‐co‐(5‐hexen‐1‐ol)) containing 50 mol‐% of 5‐hexen‐1‐ol units is an almost alternating copolymer.     

A new minor butenolide from <Emphasis Type=Italic>Machilus odoratissima</Emphasis>

A new butenolide, designated odoratinolide (1), was isolated from the bark of the Vietnamese medicinal plant Machilus odoratissima. Its structure was determined by spectroscopic analyses.     

Simultaneous Modulation of Magnetic and Dielectric Transition via Spin‐Crossover‐Tuned Spin Arrangement and Charge Distribution

Magnetic and dielectric properties have been tuned simultaneously by external stimuli with rapid and sensitive response, which is crucial to monitor the magnetic state via capacitive measurement. Herein, positive charged Fe^II ions were linked via negative charged [(Tp)Fe^III(CN)₃]^? (Tp=hydrotris(pyrazolyl)borate) units to form a neutral chain. The spin‐crossover (SCO) on Fe^II sites could be sensitively triggered via thermal treatment, light irradiation, and pressure. SCO switched the spin state of the Fe^II ions and antiferromagnetic interactions between Fe^III and Fe^II ions, resulting in significant change in magnetization. Moreover, SCO induced rotation of negative charged [(Tp)Fe^III(CN)₃]^? units, generating dielectric anomaly due to geometric change of charges distribution. This work provides a rational way to manipulate simultaneous variations in magnetic and dielectric properties utilizing SCO as an actuator to tune spin arrangement, magnetic coupling, and charge distribution.     

Ruthenocene‐Type Complexes of N‐Fused Porphyrins

Ruthenocene‐type hybrid complexes with N‐fused porphyrinato ligands, [Ru(NFp)Cp] (NFp=N‐fused porphyrin, Cp=cyclopentadienyl), have been prepared and characterized by NMR and UV/Vis/NIR spectroscopy, cyclovoltammetry, and X‐ray crystallography. [Ru(NFp)Cp] is a common low‐spin ruthenium(II) complex and shows strong aromaticity. The Ru–Cp distance (1.833 Å) in [Ru(NFp)Cp] is comparable to that in [RuCp₂] (1.840 Å). DFT calculations on [Ru(NFp)Cp] showed the unequivocal contribution of the RuCp moiety as well as the NFp moiety to both the HOMO and LUMO, constructing a three‐dimensional d–π conjugated system. The HOMO–LUMO gaps of [Ru(NFp)Cp] are insensitive to the substituents on the NFp ligand, which is illustrated spectroscopically as well as theoretically. This is in sharp contrast to the ligand precursor, the N‐fused porphyrin, in which the HOMO–LUMO gap is affected by substituents in a similar manner to standard porphyrins and related macrocycles.     

Highly soluble [1]benzothieno[3,2-b]benzothiophene (BTBT) derivatives for high-performance, solution-processed organic field-effect transistors

2,7-Dialkyl[1]benzothieno[3,2-b]benzothiophenes were tested as solution-processible molecular semiconductors. Thin films of the organic semiconductors deposited on Si/SiO2 substrates by spin coating have well-ordered structures as confirmed by XRD analysis. Evaluations of the devices under ambient conditions showed typical p-channel FET responses with the field-effect mobility higher than 1.0 cm2 V-1 s-1 and Ion/Ioff of approximately 10(7).     

Proposed mechanism for the reaction catalyzed by a diterpene cyclase,aphidicolan-16beta-ol synthase: experimental results on biomimetic cyclization and examination of the cyclization pathway by ab initio calculations

To examine the mechanism of the cyclization reaction catalyzed by aphidicolan-16beta-ol synthase (ACS), which is a key enzyme in the biosynthesis of diterpene aphidicolin, a specific inhibitor of DNA polymerase alpha, skeletal rearrangement of 2a and biomimetic cyclization of 4b were employed. The structures of the reaction products, which reflect penultimate cation intermediates, allowed us to propose a detailed reaction pathway for the Lewis acid-catalyzed cyclizations and rearrangements. Isolation of these products in an aphidicolin-producing fungus led us to speculate that the mechanism of the ACS-catalyzed cyclization reaction is the same as that of a nonenzymatic reaction. Ab initio calculations of the acid-catalyzed reaction intermediates and the transition states indicate that the overall reaction catalyzed by ACS is an exothermic process though the reaction proceeds via an energetically disfavored secondary cation-like transition state. In conjunction with the solvent effect in the acid-catalyzed reactions, this indicates that the actual role of ACS is to provide a template which enforces conformations of the intermediate cations leading to the productive cyclization although it has been believed that the cation-pi interaction between cation intermediates and aromatic amino acid residues in the active site is important for the enzymatic catalysis. This study provided important information on the role of various cationic species, especially secondary cation-like structures, in both nonenzymatic and enzymatic reactions.